Document creation > Clarify the "Extend nothing" concept

When creating a new document, you have to select if the document:

• Extends nothing (? not true since it's extending the default document behavior)
• File (if i'm new to Studio: i don't know the difference between file and document)
• Folder.
  See screenshot.

This is an important concept to understand while it's adding a lot of complexity in a simple step. And the "extend" notion is a technical notion, the label should be replaced by "inheritance" (see subtask).

To simplify it, the document creation screen should be displayed like this:
Label: bla bla
Feature ID : blabla (generated from the label but still editable)
Description: description of the new document type for Studio co-workers.
See studio_Document_creation.png screenshot.